This invention relates to stereoscopy and more particularly to viewing screen constructions for enabling perception of projected stereo pair images in seemingly three dimensional form. Such screens may be used, for example, for entertainment purposes or in other contexts such as in navigation aids in which three-dimensional shadow images are utilized to facilitate the instrument navigation of aircraft or other vehicles where the visibility of landmarks is limited or absent.
The viewing of projected stereo pair images requires that each eye of a viewer perceive only a separate one of the two images of the pair in order for the perception to be seemingly three dimensional. Where the stereo pair images are projected towards a screen, it is customary to code the light which defines one image in a first way and to code the light which defines the other image in a different way. Two different colors of light may be used for example or the light for each image of the pair may be differently polarized. To block each kind of light from a separate eye of the viewer, it has been a common practice to require that the viewer wear light analyzing eyeglasses. Such eyeglasses can be uncomfortable and may produce adverse physiological reactions. If the viewer wishes to look away from the screen momentarily, the eyeglasses impede perception of the surrounding scene unless they are removed. This can be more than an inconvenience in some forms of 3D image viewing. For example where the pilot of an aircraft is using an instrument navigation aid which presents data in the form of an artificial three dimensional shadow representation of the situation of the aircraft, it is important that the pilot be able to look elsewhere quickly and clearly.